Help with Fanuc servo motor

[rmccale]

I have a GN6 controller with Fanuc 6l dc servo motors I replaced the tach brushes and now get a 413 alarm when I try to jog that axis, when I reset it at the control the axis jumps and I get a 401 and 410 alarm. could the encoder be bad I switched the motor for the x and y and the problem follows the motor. Any help would be appreciated.

[Al_The_Man]

Sounds like an encoder, if the encoder is on the motor that is.
One way to detect bad encoder that has worked for me in the past is to disconnect the motor armature leads so the motor cannot turn.
Attempt to move the axis by HW on low rate, turn in say + direction until following error appears, when it does, read out the amount of travel it would have gone if connected, say .375".
BTW, the display shows what the desired position is, not read from the encoder.
Next reset the error and again slowly turn the HW to some value under the F.E. value, Then turn the motor shaft or ball screw the amount that correlates to the screen, i.e. if the display shows .125" then turn the motor the amount it would have turned for .125", you have to work this out from the BS or gearing.
If you keep repeatedly advancing one and then the other, the control will not detect a following error and you will know it is reading the encoder.
If you cannot do it without a F.E. appearing, it show the encoder is bad.
It sounds complicated but it has worked for me on many occasions.
Al.

[rmccale]

This is a Strippit turret punch press,I tried to disconnect the lead wires and turn the ballscrew but it just gets a 410 alarm.

[Al_The_Man]

This will happen anyway if you do not engage the HW and just turn the B.S., especially a punch as they often have very high lead BS's.
You need to follow the method exactly, but try not to turn the B.S. too much at once.
Al.

[rmccale]

I put a dial indicator on the x axis so I could be precise while turning the ball screw to match the control but keep getting a 412 error do I need to change the encoder?

[Al_The_Man]

Probably not, as it would have to read the encoder to see a 412 error!
Al.

[rmccale]

ok thanks for all your help Al. do you have any other suggestions as to my servo problem?
rick

[WGoyer]

I'm not sure that you have encoders in the 6L motors. I don't think it would have a tach if it had an encoder. Could it have a resolver? Anyway, if your problems started when you changed the tach brushes, I'd start there.
1) Put a voltmeter across the tach wires. Put the black lead on the machine's frame ground and the red lead on the tach wire that is NOT grounded.
2) Flip the ballscrew or motor in the PLUS direction. The tach voltage should go MINUS.
30 Flip it the other way and the polarity should be the same value but PLUS.

Drive systems like this are like loaded guns without the negative feedback that the tach provides. When the motor jumps out of control, the CNC shuts it down. Without a tach signal, it WILL jump out of control.

Warren
Uptime Electronics, Inc.

[rmccale]

Thanks Warren, and yes it is a pulse coder and not an encoder i'm not sure of the difference. I checked the tach across the pins in the cap and got + and - voltage but there is nothing when I go to ground unless I am not getting a good ground??????
Rick